Method and apparatus for forming structures in the ground

ABSTRACT

A method for making an elongated liquid-filled hole extending downwardly in the ground which may be used in the construction of foundation piling, water wells, sand drains, tension anchors and related installations, the method comprising generally the steps of providing a rigid, elongated drive member or mandrel having a drive foot on its lower end; forcing the mandrel drive foot through and displacing the soil to form a space with a crosssectional area greater than the mandrel stem in the wake of the drive foot; and simultaneously filling this space with a preselected liquid supplied at the ground surface, the liquid thereby flowing downwardly with the mandrel behind its drive foot. For some embodiments of the invention, the liquid is left in the hole formed where it becomes part of the body of the completed structure, such as in cast-in-place concrete piles or sand drains. The drive foot of the mandrel in all cases is left within the hole and in some instances the mandrel stem is detachable from the drive foot and is removed from the hole formed, either before or after additional liquid is applied, depending on the type of structure being built.

United States Patent Sherard 1 Feb. 1, 1972 [54] METHOD AND APPARATUS FOR FORMING STRUCTURES IN THE GROUND [72] Inventor: James L. Sherard, 70 Hillcrest Road,

Berkeley, Calif. 94705 [22] Filed: Mar. 28, 1969 [2|] Appl.No.: 812,574

[52] U.S.Cl ..6l/l1,61/35, 61/53.5, 61/5352, 61/536, 6l/53.66 [51] Int. Cl. ..E02d 3/12, E02d 5/34, E02d 5/72 [58] Field of Search ..61/11, 13, 35, 36, 53.52, 53.6, 6l/53.64, 53.66, 63, 53.5

[56] References Cited UNITED STATES PATENTS 1,570,697 1/1926 Moore ..166/230 2,140,111 12/1938 Neman ..6l/53.64 2,659,208 11/1953 Jourdain.... ..61/11 3,206,935 9/1965 Phares 61/5364 X 3,406,524 10/1968 Blenkarn ..61/53.5 3,420,063 l/1969 Bodine, Jr.. ...61/1l 3,478,524 ll/1969 Hoppe ..61/63 FOREIGN PATENTS OR APPLICATIONS 1,441,740 1966 France ..61/1 1 Primary Examiner-Jacob Shapiro Attorney-Owen, Wichersham & Erickson [5 7] ABSTRACT A method for making an elongated liquid-filled hole extending downwardly in the ground which may be used in the construction of foundation piling, water wells, sand drains, tension anchors and related installations, the method comprising generally the steps of providing a rigid, elongated drive member or mandrel having a drive foot on its lower end; forcing the mandrel drive foot through and displacing the soil to form a space with a cross-sectional area greater than the mandrel stem in the wake of the drive foot; and simultaneously filling this space with a preselected liquid supplied at the ground surface, the liquid thereby flowing downwardly with the mandrel behind its drive foot. For some embodiments of the invention, the liquid is left in the hole formed where it becomes part of the body of the completed structure, such as in cast-in-place concrete piles or sand drains. The drive foot of the mandrel in all cases is left within the hole and in some instances the mandrel stem is detachable from the drive foot and is removed from the hole formed, either before or after additional liquid is applied, depending on the type of structure being built.

14 Claims, 62 Drawing Figures sisams PATENTED FEB 3 I972 FIG 3 sum mar 10 INVENTOR. JAMES L. SHERARD ATTORNYS PATENTED FEB I 1972 SHEET UEGF I0 FlG 2g FlG2b FIG INVENTOR. JAMES L. SHERARD ATTORNEYS PATENTEDFEB H972 SHEET mar 10 PATENTED FEB 1 972 SHEET U7UF 10' IO- .-v.. .1... o a 8 w w 12 FIG 120 FIG INVENTOR.

JAMES L. SHERARD ATTORNEYS PATENTED ma H972 3.638.433

SHEET UBUF 10 k Wm INVENTOR. JAMES L. SHERARD FlG l9g /i "-1 BY 992 ATTORNEY'S PATENTEU FEB 1 I872 SHEET USUF 1O ATTORNEYS PATENTED FE 1 1972 SHEET IOUF 1O G0 0 w? 4 W N /l 2 7 xxx/ rzx/vvvv Q 2 FIG ..24;Q

INVENTOR. JAMES L. SHERARD ATTORNEYS METHOD AND APPARATUS FOR FORMING STRUCTURES IN THE GROUND This invention relates to a method and apparatus for forming elongated structures that extend downwardly from the ground surface particularly in soil deposits and utilizing the general procedure of driving or forcing a straight, elongated structural member into the earth. It also relates to various unique forms of underground structures which may be made from my improved method and apparatus, such as piling for structural foundations, sand drains and the like.

Heretofore, methods of forming holes in the ground by continuously driving a mandrel were generally limited to holes of relatively shallow depth and to relatively soft soils into which the mandrel could be forced or driven fairly rapidly and economically with construction equipment of reasonable size and power. Deep holes, such as for water wells, were always made by an excavation process using a drill rig. This was true largely because the frictional resistance or drag forces between the sides of the mandrel and the soil through which the mandrel was being driven or pushed are relatively high in most soils and absorb a great deal of energy. Particularly in dense sands and stiff clays, the mandrel used for holes for piling and other structures could only be driven slowly and to moderate depths. The present invention overcomes this main limitation of prior methods of forming holes in the ground by driving a mandrel in a manner that it greatly reduces friction between the sides of the mandrel and the soil being penetrated. Thus with driving equipment of a given size and energy, using the principles of my invention, holes can be made faster, to greater depth and larger in diameter than was heretofore possible with the prior art driving methods.

Fundamental to the present invention is the use of a rigid and straight structural member, generally referred to hereinafter as a mandrel, comprised of a stem section and a drive foot near its lower end, which drive foot has a larger area in transverse cross section than that of the mandrel stem. Hence, as mandrel is driven or otherwise forced to penetrate the ground the drive foot makes a hole in the ground which is larger than the solid body of the mandrel stem. Thus, the primary action of the first stage of forming the hole is a process of pushing, squeezing, or otherwise forcing the soil out of the underground space where it is desired to form the hole.

A second fundamental element of my method is the use of a liquid or flowable material to fill the portion of the hole not occupied by the mandrel stem as soon as the mandrel foot, which created the hole, has progressed forward. in accordance with the principles of my invention the liquid is supplied around the mandrel at the ground level, so that as the mandrel moves downwardly through the ground the liquid flows downwardly by gravity and fills the space created. This liquid surrounds or substantially surrounds the mandrel stem, thereby supporting the walls of the hole and greatly reducing the frictional drag of the mandrel as it is driven progressively downwardly into'the ground. This allows essentially all of the power and force applied to the mandrel to be transmitted to its drive foot which displaces the soil to form the hole. in the same way, the liquid greatly reduces the side friction during withdrawal of the mandrel stem from the ground. In some applications of my invention the resistance to the downward penetration is further reduced by use of a hollow cylindrical mandrel with an open drive foot which allows a soil plug to move up through the mandrel.

In my method for forming a hole in the ground according to the present invention the mandrel is caused to penetrate the ground by means of any suitable hammer or vibrator of the types commonly used for driving piling. Heretofore, even the more powerful pile drivers were only partially successful in many soils because a greater part of the energy applied was absorbed by increased side friction. In the present invention, little or no energy is lost in side friction and hence, larger and more powerful pile drivers can be used more effectively. By applying the principles of my invention, there is no practical limitation to the depth to which holes can be formed in soil deposits. For example, in sand and gravel deposits, holes with diameters in the range of 12 to 30 inches can be easily formed to depths of several hundred feet, which heretofore was practically impossible using prior art methods of driving a mandrel, regardless of the energy or design of the pile driver.

One major application of the present invention is in the construction of cast-in-place concrete piling, which can be 'made by procedures which are less costly and more rapid than prior art methods. in addition, several novel types of piling can be made which have certain specific applications and advantages.

One type of cast-in-place concrete pile is well known as an uncased" pile. Heretofore, one method for forming such piles was by driving a pipe mandrel, filling the interior of the pipe with concrete and pulling the pipe, thereby leaving the concrete in the ground. Using this technique, precautions of various types were required to assure that the concrete column left in the ground'when the pipe mandrel was pulled was continuous and contained no voids filled with soil and ground water. This type of pile was not widely used because such voids were difficult to detect and sometimes occurred in spite of the greatest construction care. Another disadvantage with this prior art method was that a relatively great pull was required to remove the pipe mandrel due to its sidewall friction with the ground.

Another common prior art method for making such uncased cast-in-place concrete piles required drilling a hole with a helical flight auger and filling the hole with a flowable concrete by pumping it down a conduit in the center of the stem of the helical auger as the auger is being withdrawn from the ground. Such methods are disclosed, for example, in US. Pat. Nos. 3,300,988 and 3,391,544. An advantage of the uncased pile made with the helical auger is that there is little or no displacement of the soil around the pile or disturbance to adjacent underground structures. However, the method of making uncased piles with the continuous flight auger has two major disadvantages. First, since the pile is not driven, it cannot be relied on to transfer any substantial load to the ground through its tip. The second disadvantage of the auger method is that occasionally piles are formed in which voids are created in the concrete, a defect which occurs when the auger is pulled out of the ground at a rate greater than the rate at which the concrete is pumped down into the hole.

Using the method of the present invention, uncased cast-inplace piles can be made which are less costly than piles made by either of the two prior art methods described above and which eliminate the serious problems and disadvantages of these methods. In particular, my method removes any possibility of creating voids in the concrete pile during the withdrawal of the mandrel or casing.

Cast-in-place concrete piles of the type in which a thin steel shell is driven into the ground and concrete poured in later have also been widely used. With this type of pile it is possible to leave the shell unfilled until most of the piles in the general area are driven into the ground and then to inspect each ernpty shell immediately before filling it with concrete. Thus, the engineer can be confident that any given pile in an area is not damaged by the subsequent driving of the neighboring piles. In order to save the cost of the steel shell it was long an aim of the industry to find a method for constructing a cast-inplace pile of this type using concrete for the shell. Methods, heretofore proposed, for making such cast-in-place concrete shells were too costly. The present invention solves this problem by providing a method for making cast-in-place concrete shells at less cost than steel shells.

Another problem which is solved by the present invention is that of driving a pile into a layer of dense sand. In the prior art practice, it was extremely difficult to drive a pile more than a very short distance into such a layer because the dense sand offered very great resistance to the pile. As a practical matter, concrete piles and pipe piles with closed ends could not be driven more than a few feet into such sand layers before reaching refusal with a conventional pile driver of moderate size. in such circumstances, where it was desired to have the 3 piling penetrate further so-called nondisplacement" piles such assteel H-beams, and in some cases open ended pipe piles, were utilized. Even with steel l-l-piles, the driving was frequently very slow and difficult and there was always the great technical disadvantage that the pile might be deflected and bent back upward during the hard driving without the fact beingknown. An open ended pipe pile in such a circumstance might drive somewhat easier than a closed pipe, since some of the sand enters the interior of the pipe; however, after a plug of a few feet of sand has entered the lower end of the pipe, this frequently became so tightly jammed in place that no further sand could enter and the pile acted henceforth as a closed end pile. Using the principles of my invention, it is possible to overcome this problem. and to install piling relatively easily and rapidly to considerable depths into layers of dense sand.

The methodof the present invention is particularly well adapted for the formation of friction piling designed for very heavy loads. For example, where a structure is to be founded on piling which is driven a short distance into a thick layer of dense sand and gravel, precast or cast-in-place concrete piles with tip diameters in the range of 8 to 14 inches are commonly driven to [5 feet into the layer and designed for loads of 50 to 75 tons. They are not driven deeper because they reach essential" refusal. In such a circumstance, if a high energy hammer is used the driving resistance may be adequate to justify the use of a high design load. For example, the pile may be driven to a final penetration resistance of 5 to blows per inch with a hammer delivering an energy of 60,000 footpounds, per blow which would give a calculated bearing capacity, using one of the widely accepted equations for calculation, of from 200 to 300 tons. In spite of these high indicated bearing capacities, because the pile only penetrates the sand and gravel bearing layer a relatively short distance, most engineers would hesitate to use the pile to carry more than about 75 tons. However, using the methods according to my invention, piles can bedriven into the dense sand and gravel layer much further, such as to 30 feet, so that there is nodoubt that they can be designed safely to carry very high loads, such as for example 300 to 600 tons or 5 to 10 times the load commonly used in the prior art practice. This provides a great saving in the cost of the piling and, in addition, in the cost of the pile cap used to connect the piles at their upper ends with the building being supported.

Vibrating drivers for installing foundation piling which vibrate the pile longitudinally hundreds or thousands of times per minute have proved to be particularly effective for installing piles in deposits of sand below the water table. This is because the vibrations cause the sand along thesides of the piling to liquify" partially as the pile is being sunk, thereby allowing most of the driving energy to be transmitted directly to the tip of the pile where it is most effective. For stiff clays and some other types of soils, however, vibrating drivers do not work well because the side friction between the walls of the piling and the soil absorbs the greater part of the driving energy. Hence, for stiff clays, and some other kinds of soils, conventional pile driving hammers which deliver heavier blows at less frequent intervals are much more effective than the newer vibrating equipment. Using the techniques of the present invention, in which the friction between the sides of the piling and the soil through which the pile is driven is removed, such vibrating drivers can be used equally effectively in clay as in sand.

In sands the vibrating drivers install piling much more rapidly than conventional hammers, such as operated by steam or diesel power. When driving piling according to the principles of my present invention, conventional steam and diesel hammers are much more efficient in sand deposits and compete very well with the performance of vibrators.

Heretofore, when driving long piling through stratified soil to bedrock or to a deep bearing layer of soil using the prior art methods, the sides of the piling had a tendency to hang up on a resistant intermediate soil layer. When this happened it was difficult for the engineer to evaluate how much of the final driving energy of the hammer was effective in seating the tip of the pile into the surface of the bearing layer and how much energy was being taken out by the upper resistant layer. In such a circumstance, it often became necessary to predrill holes for the piling or to "jet the piling to remove the resistance to driving of the intermediate layer. When driving piling according to the method of the present invention, the side friction is removed automatically and it is never necessary to predrill or to jet holes in advance of pile driving.

Cast-in-place concrete piling were commonly made in prior art practice by driving a thin steel shell into the ground with a rigid, closely fitting mandrel. After driving to the depth desired, the mandrel was pulled and the shell was filled with concrete. One' of the problems which arose with this kind of piling was that occasionally the thin steel shell was torn or otherwise damaged by the driving operation, allowing ground water to penetrate-the shell. Using methods according to the principles of the present invention, cast-in'place concrete piles with thin steel shells can be installed with no possibility of damage to the thin shell, so that-the shells can safely be made thinner and less expensive.

In deep deposits of clays and'silts, the loads which can be carried by friction piling are determined largely by the shear or bond which may develop between the soil and the exterior surface of the piling. Hence, it is highly desirable to have as much peripheral area as possible and to have a rough and irregular surface. Using the principles of the invention, cast-inplace concrete piling with longitudinal ridges on the exterior surface capable of developing greater side shear or bond per unit of length of pile, can be formed much more easily and economically than by current art methods. I

It has long .been known that very slender steel piles can carry loads without buckling even when the soil through which they are driven is a very soft material; that is, the lateral support given by even a very soft mud is adequate to allow the steel to sustain the compressive stresses which can be carried in a short column. This fact makes the use of very thin steel piles, such as railroad rails and even reinforcing bars, theoretically quite attractive in a situation where piling is to be driven through a thick deposit of soft soil to the upper surface of the hard bedrock. Suchpiles have been used to a limited extent. The main technical disadvantage and the reason that they are not used more frequently, is the inherent difficulty of driving the thin piling in such a way that it will be straight and vertical at the end of the driving process. A general disadvantage of steel piling, and particularly of thin steel sections, is the hazard of corrosion. The present invention makes it practical to install very slender steel piles in the ground in a way that gives complete confidence that the installed pile is vertical and straight and that the steel pile is encased in a jacket of concrete to increase its strength and prevent corrosion.

One of the occasional problems with foundation piling was that the long time settlement of an upper layer of soil gradually caused a downdrag on the piling, and eventually excessive settlement of the piling. With the present invention a novel type of pile can be made which has an annular mudfilled space around its upper portion so that settlement of the ground cannot cause any appreciable downdrag on the piles.

In many cases when driving piling through a soft soil layer at the surface into an underlying bearing layer such as a layer of medium dense sand, it is difficult to judge in advance how deep the piles will have to be driven into the underlying sand bearing layer. Usually the piles are driven to a certain driving resistance with a hammer of a certain size. A problem frequently arose using wood or precast concrete piles, for example, where many of the piles ordered for the job were not long enough to reach the desired driving resistance. In the present invention where the drive foot is detachable from the mandrel, this problem is overcome by the selection of a drive foot of the proper size. For example, if a pile with a given length does not reach the desired or specified driving resistance by the time it is driven into the ground, using the method of the present invention a larger drive foot can be installed on the mandrel stem for the subsequent piles so that the driving resistance will be higher, and the specified value will be achieved before the pile has penetrated to its full length. My invention thus provides more flexibility in this regard than any prior art method. For example, it is well known that the driving resistance of a pile in most soils increases greatly with the area of the tip of the pile; therefore, small differences in the diameter of the drive foot have a large influence on the driving resistance of the pile. Drive foot members having a particular configuration and made of certain materials can be used in soil conditions where each is best suited.

Another application of my invention is in the construction of water wells. Heretofore, except for wells of very shallow depth, all water wells were put down by drilling procedures. l-loles'for water wells in soil deposits were not formed by driving a mandrel in the ground because it was not generally possible, using prior art methods of driving a mandrel, to get holes of adequately large diameter for wells down to the necessary depths. However, with my invention, holes in soil can be formed to the dimensions needed for wells much more economically by driving a mandrel than by drilling.

All prior art methods for forming water wells in the ground included the steps of drilling the hole, holding the hole open temporarily, installing the casing, and backfilling outside the casing with a filter material. With my invention it is possible to form water wells in the ground in which several or all the above individual steps are carried out in one single continuous operation.

In prior procedures for drilling water wells in soil formations which contain large gravels and cobbles it was necessary to break or grind up the larger rocks with the drill bit before the material was removed from the ground, a process which was slow and costly. With my method it is unnecessary to break down or chew up these larger rocks in order to form the hole for the water well, and this provides a great saving in time and cost.

For large diameter wells in sand and gravel formations the process of drilling called reverse rotary was commonly used in which the drill water was circulated down the hole and the drill cuttings and return drill water came up the interior of the drill stern. A fundamental disadvantage with this method was that the hole was constantly filled with water and it was not possible to obtain any indication during the drilling operation of the water-producing capability of the well from sand or gravel layers at various specific elevations. This was a large disadvantage since it did not allow any reliable estimate to be made from observations during construction of the well of the amount of water flowing into the well hole at a given depth. The present invention provides a method for constructing water wells which is superior to the reverse rotary method from the standpoints of speed and economy and at the same time allows an indication to be obtained of water flow into the well at each level during construction.

Yet another application of my invention is in the construction of sand drains. Thick deposits of soft, saturated silt and clays are sometimes consolidated and made stronger and better able to support superimposed loads by the installation of sand drains which are vertical, cylindrical sand columns installed in closely spaced holes formed in the soft soil deposit. Heretofore, such holes were frequently made by simply driving and pulling a cylindrical sand filled mandrel. This procedure had two main disadvantages. First, the driving and pulling procedure created a thoroughly remolded skin or smear of impervious soil on the walls of the hole, which skin acted to reduce the rate at which water could flow from the pores of the soft clay deposit to the sand drains. Second, the penetration of the closed end mandrel displaced the soft soil by pushing it to the side which had the disadvantage that natural structure of the soil was disturbed. This was undesirable for many soft silts and clays because it increased the compressibility of the material and decreased its permeability.

In an effort to overcome the soil disturbance caused by displacement, several construction techniques were developed for sand drains including methods in which the soil was removed from the ground by a continuous flight auger and others in which the soil to be occupied by sand drain was removed from the ground inside an open ended pipe as disclosed in U.S. Pat. No. 3,358,458. in both of these methods, however, the thin layer of soil comprising the walls of the sand drain was badly remolded and smeared, by the rotating auger in the former method and by driving and pulling the open ended pipe in the latter method. Using the principles of the present invention, said drains can be installed with no appreciable disturbance of the structure of the soil outside the volume of the sand drain and without forming a skin of remolded soil on the walls. Also, the principles of the present invention permit the construction of a novel type of sand drain consisting of a small diameter sand column with an interior porous tubing, which has both technical and economical advantages over prior art drains.

in heavy construction projects, tension anchors or tiebacks have been used both for temporary supports for bulkheads and temporary retaining walls and for permanent anchors to hold down certain kinds of structures such as high towers against uplift from wind pressures and earthquake. in all prior art methods for installing such anchors, the activities of holding the hole open and of grouting or concreting the space around the tension rod or cable are carried out in two separate steps. Using the principles of my invention, anchors are installed by a method which combines both of these main steps in one simple operation and hence anchors can be installed more rapidly and more economically than by current art methods.

It is often necessary to install an open cylindrical casing, such as a steel pipe, within a hole in the ground and to cement it in place by filling the annular space between the outside surface of the pipe casing and the walls of the hole with concrete. Such cemented-in-place casings are used for a great number of diverse purposes among which are sealing the upper part of a water well, as shells for cast-in-place piles or concrete piers; as foundations for poles which protrude vertically out of the ground, such as are used for street lights and signs; hydraulic shafts for elevators; casings for the installation and operation of instruments below ground such as slope indicators and piezometers. In the current art such installations are made by drilling a hole in the ground, holding the hole open temporarily, installing the casing and finally filling the exterior annular space with concrete, grout or other cementitious material. Using the principles of the present invention, a casing can be installed in the ground and cemented in place, in one continuous process without the individual separate method steps of the current art.

The principles of my invention may also be applied in the solidification of large ground areas. Heretofore, masses of soil below ground were solidified by a process of grouting which generally included the steps of drilling injection holes, installing steel casing and/or injection pipes in the holes, injecting the fluid grout, usually a cementitious chemical, and finally pulling the casing. Using the method according to the present invention the same result can be achieved with all the method steps being combined in one simple continuous operation which is more efficient and economical.

For certain engineering purposes it is sometimes highly desirable to obtain continuous undisturbed cylindrical samples of a deposit of soft silt or clay from top to bottom, taking individual samples with a length of 20 to 50 feet, for example. Heretofore, this was extremely difficult to accomplish in a reliable fashion. lt was not possible to do it by simply pushing an open ended, thin walled pipe into the soil formation, primarily because the friction between the soil sample and the interior of the pipe make it necessary to use considerable force to push the pipe in the ground and this created an unacceptable disturbance of the natural structure of the soil. The only reliable prior art method for taking such a sample was with an apparatus called the Swedish Foil Sampler, in which thin metal strips or foils were unrolled as the pipe was pushed into the ground using a technique such that the foils separated the soil sample inside the pipe from the inside walls of the pipe and there is no relative movement of metal and soil. However, this method was not widely used, primarily because of the relatively intricate and expensive apparatus required. With the presentinvention, very good continuous, undisturbed samples of soft soil deposits can be obtained relatively easily.

In accordance with the foregoing, it is, therefore, a general object of my invention to provide a method for making holes in the ground by the procedureof driving or forcing a structural member or mandrel into the ground and displacing the soil in its path, which method overcomes the problems and disadvantages of the prior art methods, is faster in practice and more economical in labor and materials and allows holes to be made with a larger diameter and to be put to greater depths than was heretofore possible with prior art methods.

Another object of the invention is to provide a method for making holes in the ground by the procedure of driving or forcing a structural member, such as a cylindrical mandrel, into the ground and displacing the soil in its path that eliminates or greatly reduces the side friction between the structural member and the ground and permits all the force and energy applied to the upper end of the structural member to be effective at its lower end so as to cause it to penetrate the ground rapidly and efficiently.

Another object of the present invention is to provide a method of driving piling into the ground for foundations of structures in which the walls of the piling or of the mandrel are separated from the. ground by a thickness of liquid, such as concrete, grout or mud, in such a way that the side friction during the driving is greatly reduced and most of the energy of the pile driver is transmitted to the lower tip of the pile.

Another object of the present invention is to provide a method of making an uncased cast-in-place concrete piling which overcomes the deficiencies of prior art methods.

Another object is to provide a method of making a type of uncased concrete piling at a lower unit cost than was possible with any prior art method and particularly at a cost which is lower than that of wooden piling.

Another object is to provide a method of constructing castin-place concrete piling using a cast-in-place concrete shell which can be left open and inspected before the main body of the piling is poured.

Yet another general object of my invention is to provide a type of piling which can be driven through stiff clayey soils with a vibrating pile driver more rapidly andeconomically than is possible with prior art methods.

A main object is to provide a method of making a cast-inplace reinforced concrete friction pile capable of supporting loads of 200 tons or more.

Still another object of the present invention is to provide a type of piling which can be driven into sand deposits by conventional pile driving hammers at a more rapid rate than heretofore possible using prior art methods.

Still another object is to provide a method for installing a foundation into a layer of dense sand to depths not practical with prior art methods of pile driving.

Yet another object of the present invention is to provide a method for making concrete friction piling, particularly for use in deep deposits of clay and silt, with an irregular exterior surface which develops larger side shear forces per unit of pile length than prior art piles.

Still another object is to provide a method of forming castin-place concrete piling using a thin steel shell in which there is no danger that the shell will be damaged by the driving operation and in which a thinner, less costly, shell can be'used.

Another object is to provide a method of installing very slender and long steel piling in a way that assures that it is both vertical and straight, and the problems of corrosion is eliminated.

A further object is to provide a means for constructing several new types of piling which are useful for special applications such as a composite pile consisting of a central core of wood and a jacket of concrete. Other noveltypes of piling constructed according to the principles of the current invention are a precast concrete pile and a pipe pile each cemented in place in the ground with an outer jacket of cast-in-place concrete. Another novel piling has an annular mud-filled space around its upper part in order to prevent downdrag loads as the result of settlement of the upper soil layers.

Other miscellaneous objects in connection with the installation of foundation piling are: (l) to eliminate the hazard that ground water which enters the hole may weaken the freshly placed concrete forming the body of cast-in-place pile; (2) to eliminate the need for predrilling and jetting in advance of driving the piling; and (3) to make the final driving resistance of the piling (that is, in terms of number of blows of the hammer per inch of penetration of the pile) a better indicator of the nature of the material directly below the tip of the pile and thus the load which can safely be transmitted to the end of the pile. 7

It is a further general object of the present invention to provide a method for making holes in the ground by driving a mandrel which will be generally satisfactory for the formation of water wells and which will be less costly and allow more rapid construction than prior art methods.

A further object of the present invention is to provide a method for forming water wells in which some or all the main individual construction'steps of the current art procedures, such as drilling the hole, supporting the walls of the hole temporarily, installing the well casing and backfilling the casing with graded filter sand are combined into a fewer number of simple steps.

Another object of the present invention is to provide a method for forming water wells in which it is not necessary to break or grind up coarse gravels and cobbles before they are removed from the ground, as was necessary in prior art methods.

It is a further object of the present invention to provide a method of forming holes for water wells in the ground in which it is possible at each level of penetration of the hole during its formation to obtain a measure of the quantity of water which it will be possible to pump from the soil at this level.

Still another object of my present invention is to provide a means for installing steel tieback anchors in soil deposits more rapidly and economically than possible with prior art methods.

Another major object of my invention is to provide a method of making sand drains in soft andv water-logged deposits of silts and clays which are more effective in causing rapid consolidation of the soft deposit than any drain constructed by prior art methods.

Still another object is to provide a method of making a novel type of sand drain with a small diameter, flexible, porous tubing inside.

Another object of the current invention is to provide a method for installing open pipe casings in the ground and cementing them in place withconcrete which is cheaper and more rapid than any method of the current art.

Another object is to provide a method for solidifying masses of soil below ground by the injection of cementitious grouts which is cheaper and more rapid than prior art ground solidifying methods.

Other objects, advantages and features of the present invention will become apparent from the following detailed description of both the method steps and the apparatus for performing the method taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view in elevation and in section of a hole being formed in the ground using the principles of the present invention;

FIG. 1a is a plan view in section taken along line la-la of F l0. 1;

FIG. 1b is a view in elevation and in section similar to FIG. 1 showing the mandrel stem detached from its drive foot and partially removed from the liquid-filled hole;

FIG. 2 is a view in elevation and in section of another embodiment of my invention utilizing a hollow, cylindrical mandrel with a detachable, concrete drive foot;

FIGS. 2a-2c are views similar to FIG. 2 showing the steps of constructing an underground piling structure;

FIG. 3 is a view in elevation and in section of another embodiment of my invention utilizing a mandrel with an enlarged end portion and a detachable drive foot;

FIG. 3a is a fragmentary view similar to FIG. 3 showing the mandrel partially removed;

FIG. 4 is a schematic view in elevation and in section of another form of apparatus for making underground structures according to the principles of my invention in which the soil in the path of the downward penetrating drive foot is forced to enter the center of a hollow pipe mandrel;

FIG. 4a is a schematic view in elevation and in section similar to FIG. 4 showing the hollow pipe mandrel filled with earth and being withdrawn from the ground;

FIG. 4b is a fragmentary view in elevation and in section of a modified form of apparatus similar to FIG. 4;

FIG. 5 is a schematic view in elevation and in section of a modified form of apparatus utilizing a perforated pipe mandrel;

FIG. 6 is a schematic view in elevation and in section of an apparatus according to my invention utilizing a perforated sleeve around the mandrel;

FIG. 6a is a view in section taken along the line 6a-6a of FIG. 6;

FIG. 7 is a schematic view in elevation of a piling formed in accordance with the present invention utilizing an H-beam mandrel;

FIG. 7a is a view in section taken along the line 7a-7a of FIG. 7;

FIG. 7b is a view in section of a modified form of H-beam mandrel having an irregular drive foot;

FIG. 8 is a view in elevation and in section of a piling formed in accordance with the present invention utilizing a precast concrete mandrel and foot;

. FIG. 8a is a view in section taken along the line 8a-8a of FIG. 8;

FIG. 9 is a view in elevation and in section showing an embodiment of my method wherein a lighter fluid is displaced by a heavier fluid in the hole formed in the ground;

FIG. 9a is a view similar to FIG. 9 showing the mandrel partially removed;

FIG. 10 is a view in elevation and in section of another form of composite piling utilizing the principles of my invention;

FIG. 11 is a view in elevation and in section of another embodiment of my invention utilizing an elongated drive foot;

FIG. 11a is a view in section taken along line llalla of FIG. 1 1;

FIGS. 12 and 12a are views in elevation and in section showing the installation of one form of composite piling in ac cordance with the present invention;

FIG. 13 is a view similar to FIG. 12a showing a modified form of composite piling;

FIGS. 14 and 14a are views in elevation and in section showing a method for making an underground structure according to the present invention using a tapered mandrel;

FIG. 15 is a view in elevation and in section illustrating a method of making a tensioning anchor utilizing the principles of the present invention;

FIG. 15a is a view in elevation and in section of the completed tensioning anchor;

FIG. 15b is a view in section of a slotted pipe mandrel for use in installing the tensioning anchor of FIG. 150;

FIG. 156 is a view in section taken along the line 15c15c of FIG. 15;

FIG. 1511 is a view in section taken along the line I5d-- 15d of FIG. 15a;

FIG. 15e is a view in elevation and in section of a modified form of the tensioning anchor of FIG. 15;

FIG. 16 is a schematic view in elevation and partially in section illustrating the installation of tensioning anchor in a side hill utilizing the present invention;

FIG. 17 is a fragmentary view in elevation and in section showing a modified form of drive foot;

FIG. 17a is a view in plan section taken along line 17a 17a of FIG. 17;

FIG. 18 is a schematic view in elevation and in section illustrating another apparatus according to my invention utilizing a thin shell with a hollow mandrel;

FIG. 18a is a view similar to FIG. 18 showing the apparatus with the mandrel removed;

FIG. 18b is a fragmentary view in elevation and in section of another modified form of apparatus utilizing a shell inside a hollow mandrel;

FIG. 19 is a schematic view in elevation and in section showing another embodiment of my method utilizing a hollow mandrel and an air stream for removing debris from the hole;

FIG. 19a is an enlarged fragmentary view in elevation and in section of the apparatus of FIG. 19,

FIG. 19b is a view in section taken along line 19b--l9b of FIG. 19;

FIG. 19c is a view in section taken along line I9cl9c of FIG. 19;

FIG. 19d is an enlarged view in elevation and in section of the upper end portion of the apparatus of FIG. 19;

FIG. l9e is a plan view in section cut on line l9e-l9e of FIG. 19a;

FIG. 19f is a view in section taken along line 19f-l9f of FIG. 19b; 7

FIG. 19g is an enlarged fragmentary view in elevation and in section of an alternate type of drive foot for the apparatus embodiment of FIG. 19;

FIG. 20 is an enlarged fragmentary view in elevation and in section showing a modified form of the apparatus for carrying out the method shown in FIG. 19;

FIG. 20a is a view similar to FIG. 20 showing the mandrel partially removed;

FIG. 21 is a fragmentary view in elevation and in section showing a form of sand drain constructed according to the present invention;

FIG. 21a is a view in section taken along line 2la-2la of FIG. 21;

FIG. 22 is a fragmentary view in elevation and in section of another form of mandrel and drive foot combination utilizing the principles of the present invention;

FIG. 22a is a view in section taken along line 22a22a of FIG. 22;

FIG. 23 is a schematic view in elevation and in section showing another mandrel and drive foot apparatus according to my invention;

FIG. 23a is a view in section taken along line 23a23'a of FIG. 23;

FIG. 24 is a view in elevation and in section of another embodiment of my invention primarily useful for making a thin cast-in-place concrete shell;

FIG. 24a is a view in section taken along line 24a-24a of FIG. 24;

FIG. 24b is a view in elevation and in section of a cast-inplace concrete shell made with the apparatus of FIG. 24; and

FIG. 24c is a view in section taken along line 24c-24c of FIG. 24b;

GENERAL DESCRIPTION OF HOLE-MAKING METHOD While I have shown the various steps of my method and also certain embodiments of the apparatus for carrying out the method, it is to be understood that these illustrations are not intended to limit the invention but are presented merely to illustrate its application in thefortns shown.

In broad terms my method for forming elongated underground structures comprises the steps of creating a space in the ground by driving or forcing a mandrel means with an enlarged drive foot into the ground and simultaneously filling said space with a liquid. In most applications the drive foot remains in the ground and the mandrel means is subsequently withdrawn as more liquid is added simultaneously to replace the volume of the withdrawn mandrel. For some applications the mandrel means is left in the hole and incorporated as part of the structure being built. The aforesaid general method steps will be better understood as they are explained in greater detail below together with a description of the apparatus and the resulting structures that are formed according to my invention.

Referring to the drawing, FIGS. 1, la and lb show method steps common to many applications, in which a hole 30 is formed through a soil deposit 32 extending from the ground surface 34 down to the upper surface of a bedrock layer 36, using one form of apparatus according to my invention. The apparatus comprises a solid, straight cylindrical mandrel stem 38 which is driven into the ground by a suitable pile driver 40, such as the kind normally used for installing foundation piling. Attached to the lower end of the mandrel stem is an enlarged shoe or drive foot 42 having a diameter greater than the mandrel stem 38. The diameter of the hole so formed is, therefore, approximately equal to the diameter of the foot and larger than the diameter of the mandrel stern. In this embodiment the drive foot is essentially a cylindrical sleeve, such as of cast steel, having a flat end 44 and the mandrel stem fits slideably within the sleeve so that it can be easily detached from it.

An annular space 46 formed between the walls of the hole 30 and the mandrel stem 38 is always kept filled with a liquid material 48. In the most common method embodiment of the current invention, as shown in FIG. 1, this liquid flows down into the hole from a small reservoir 50 which may be created on the ground surface by a tanklike structure 52. Thus, as the mandrel is being forced downwardly, the annular space 46 is constantly filled with the liquid 48 from the reservoir 50 and the mandrel stem 38 is thus surrounded by liquid. As the mandrel moves downwardly the liquid also flows downwardly by gravity and it holds back the earth walls of the hole and prevents frictional contact between the earth and the mandrel stem. The surface reservoir is replenished through a pipe or hose from a suitable source such as a tank truck 54.

For some applications, such as a foundation piling, the structure is completed when the mandrel has been driven to the depth desired and both the mandrel and the drive foot are left in the ground. Alternatively, after the drive foot 42 reaches the depth desired for the bottom of the hole, such as the bedrock surface 36 in FIG. lb, the mandrel stem 38 may be pulled. In the apparatus embodiment in FIG. 1 the lower end of the mandrel merely fits within the sleevelike drive foot 42 so that the mandrel stern will detach itself from said drive foot when it is pulled upwardly, and the drive foot, which is generally held tightly by the surrounding soil, remains in place at the bottom of the hole as shown in FIG. lb. As the mandrel stem is being pulled, additional liquid flows downward into the hole from the surface reservoir 50 to replace the volume of the mandrel being withdrawn. The pressure head at every point in the fluid filled hole 30 is essentially equal to the elevation of the fluid surface in the reservoir 50. Once the mandrel is completely withdrawn from the ground, the desired hole is completed.

The mandrel is withdrawn at a uniform and not excessively rapid rate, such as about to feet per minute, in such a way that the liquid can flow downward in the annular space, FIG. lb, at a moderate velocity and the pressure in the liquid is always well above the exterior ground water pressure. Hence, there is no tendency for the ground water to flow into the hole or for the walls of the hole to be unstable.

Since the mandrel stem is surrounded by liquid as it is being pulled, there is no frictional resistance between the mandrel and the soil. Hence, the upward force needed to withdraw the mandrel from the hole is only the weight of the mandrel, less the buoyant uplift. In fact, in some embodiments, in which a lightweight hollow mandrel is used with a closed bottom, the upward buoyant force of the liquid in the hole is sufficient to float the mandrel upward.

A major advantage of my hole-forming method according to the present invention is that the walls of the hole are generally supported by the liquid and not by the structural mandrel. Hence, as the mandrel is pulled there is no transfer of the pressure exerted on the wallsof the hole from the mandrel to the liquid. In almost all prior art methods of pulling a driven steel casing and leaving a liquid-filled hole behind, the casing itself supported the soil walls and kept the ground water out until the moment that the casing was removed, at which moment the support function was transferred abruptly to the liquid in the hole. This rapid transfer sometimes caused a collapse of the hole, which danger is eliminated by the methods of the present invention.

In FIGS. 2-2c, a variation of my method for constructing an underground structure according to the present invention is shown using an apparatus which is particularly useful for forming certain kinds of concrete piling or piers. Here, the mandrel stern 38a is a hollow cylindrical steel cylinder or heavy walled steel pipe which has a detachable drive foot 42a, made of precast concrete, at its lower end. This drive foot has a main body with an outside diameter considerably larger than the mandrel stern, and it tapers to a smaller diameter at its lower end. A central cylindrical boss portion 56 on its upper end has a smaller diameter so that it can fit within and plug the lower end of the mandrel stem 38a when themandrel is forced downwardly. Suitable sealing rings 58 between the boss por tion and the inside of the mandrel stem are provided to prevent any passage of liquid into the mandrel. As in the arrangement shown in FIG. 1, the mandrel stern 38a can be propelled downwardly by a suitable pile driver, its drive foot 42a forming an annular space 46 around the outside mandrel stem as it proceeds. A liquid, such as a flowable cementitious mortar, is supplied to a reservoir 500 which is formed in the ground around the upper end of the mandrel so that the liquid will flow downwardly around the mandrel, continuously filling the annular space. When the drive foot reaches the desired depth, as shown in FIG. 2a, the hollow mandrel stem is completely surrounded by liquid, but the inside is dry and clean so that it can be readily inspected before it is filled with liquid, which again may be a flowable concrete, by pouring it in through a pipe or hose at the upper end of the mandrel, as shown in FIG. 2a.

In some applications, such as a concrete-filled pipe pile, the mandrel is left in the hole and the structure is completed when the center is filled with concrete. In other applications, the mandrel is removed from the hole by being pulled upwardly, as shown in FIG. 2b,v a small further quantity of liquid being added to replace its volume as it is withdrawn from the ground. When the mandrel stem has been removed, steel dowels 53 or some other fittings for connecting the completed piling to the superstructure can be installed before the concrete hardens. The procedure shown in FIGS. 2-2c is particularly illustrative of the advantages of my invention because it provides for ease, rapidity and economy of installation as well as unique safety and reliability factors due to the fact that the hollow mandrel, once driven, can be inspected before concrete is poured into it, so the main portion of the piling is wholly free from any contaminating and strength reducing water or dirt.

In the procedure illustrated in FIGS. 2 and 2b, I have shown the same liquid being used outside and inside the pipe mandrel. For other applications, as discussed later herein, I may use difierent. liquids inside and outside. Also, in FIGS. 2 and 2b, I have shown the liquid reservoir 50a at the surface to be in the form of a hole dug in the ground. This hole may be small (e.g., 30 inches in diameter and 24 inches deep) and can be dug by any conventional means. Alternatively, a large hole may be provided by using an auger with a diameter between 24 inches and 48 inches which can excavate to any initial depth desired (e.g., to feet). In addition to serving as a reservoir, when used to form a concrete pile or pier, the hardened concrete therein forms an enlarged upper end which may be particularly useful as a connection with the building column because of its ability to resist lateral as well as vertical loads.

In FIG. 3, another apparatus for making holes according to my invention is shown, which comprises a mandrel stem 38b with an enlarged section in the form of a piece of very heavy walled steel pipe which is rigidly and permanently attached to the lower end. Here, when the mandrel is pulled after the hole is completed to the depth desired, the enlarged section is also pulled out of the hole. As in the previous applications the annular space 46 formed in the ground during the downward penetration of the mandrel is constantly filled with a liquid 48 which travels downward from the surface reservoir 50. As the mandrel is being driven the central channel 55 through the mandrel stem is blocked at its lower end by a precast concrete drive foot 42a, with an exterior diameter equal approximately to the exterior diameter of the lower enlarged section 60 of the mandrel stem. Next, the hollow interior of the mandrel is filled with liquid by pouring it in from the surface, and the mandrel is then withdrawn from the ground as shown in FIG. 3a leaving the hole filled with the liquid placed inside the mandrel. In this embodiment of FIGS. 3 and 3a, the hole is reamed to the full diameter again as the enlarged section of the mandrel is withdrawn. This acts to counter the tendency in some soils for the hole to decrease in diameter after the enlarged end on the mandrel has passed through. As the mandrel is withdrawn the liquid in the annular space 46 is forced upward and out of the ground.

It is apparent that liquid added to the hole as the mandrel is being withdrawn as in FIG. 3a, can also be supplied down the center of the mandrel under pressure with a pump (not shown). If the liquid pressure is made great enough it will push the mandrel out of the hole, thereby eliminating the necessity to apply an upward pull to the mandrel to withdraw it from the ground. In several important applications of my method the mandrel is forced out of the hole in this way by the liquid pressure in the hole acting upward on the bottom of the rising enlarged section 60.

FIG. 4 shows yet another embodiment of the present invention wherein a mandrel 38c consists of a heavy steel pipe which is open at the bottom so that a portion of the soil in the path of the downward penetrating mandrel is taken inside in the form of a soil plug 62. In this embodiment a drive foot 420 on the lower end of the mandrel stem is a simple annulus or ring which is very similar to the drive foot shown in FIG. 1, except that it has a hole in the center. Also in the embodiment of FIG. 4, I have shown another short length of steel pipe 64 or internal ring welded securely to the lower end of the pipe mandrel on the inside, which serves several functions. It stiffens and strengthens the lower end of the pipe mandrel and it causes the soil plug 62 to have an outside diameter which is somewhat less than the inside diameter of the'pipe mandrel 38c, thereby allowing the plug to enter without great frictional resistance.

In some applications, such as when used to form a pipe pile in the ground, the mandrel of the embodiment of FIG. 4 is simply driven to the depth desired and left in place. In these applications the soil plug 62 may be left inside the pipe mandrel or it may be removed by any of several procedures well known in the current art which it is not necessary to describe here, such as washing it out with water jets or digging it out with an auger. When the soil plug is so removed the interior of the pipe is generally, but not necessarily, filled with concrete.

In most applications the mandrel stem is withdrawn from the hole as shown in FIG. 4a and the space below ground formerly occupied by the mandrel stem and the soil plug 62 is filled by an additional supply of liquid flowing downward in the annular space between the mandrel and the walls of the hole, as shown in FIG. 4a. The end result in this case, as in the embodiments shown in FIGS. lb and 2b is a fluid-filled hole with the detachable drive foot 42c left in the bottom. In these applications, the soil plug 62 is carried out of the ground inside the pipe mandrel 380. It does not fall out as the mandrel is being lifted because it is wedged in the bottom against the internal ring 64. Once the mandrel is completely out of the hole, the soil plug can be removed from the interior by any suitable method known to those skilled in the art. For example, when a vibrating type driver is used to force the mandrel into the ground, the vibrator is turned off when the mandrel is being withdrawn from the ground in the step of FIG. 4a. Then, when the mandrel is completely above the ground and hanging freely from the crane boom, the vibrator is turned on causing the soil plug 62 to drop out of the mandrel.

In a variation of this latter embodiment of my invention, as shown in FIG. 411, I provide a series of holes 66 in the walls of the pipe mandrel a short distance above the bottom so that the liquid in the outer annular space flows through these holes into the interior of the mandrel, filling the inner annular space 68 surrounding the soil plug 62 and further reducing the friction between the soil plug and the inside of the mandrel.

The embodiment of FIG. 4 has two general potential advantages over the embodiment of FIG. 1 for certain applications. First, using a given pile driver, the apparatus of FIG. 4 with the hollow mandrel 38;", will penetrate a dense or resistant soil much more rapidly and to a greater depth than the apparatus embodiment of FIG. I. This is true because the resistance to penetration of the mandrel foot is much less in the case of FIG. 4 since it is easier to take the soil inside the mandrel than it is to push it to the side. For this same reason holes of much larger diameter can be made than are possible with apparatus in which a closed end drive foot is used. A second major difference between these two main embodiments is in the disturbance of the soil formation. In most fine-grained soils, such as clays or silts, if a considerable number of closely spaced holes are put down in a given area using the closed end mandrel, a considerable portion of the total volume of soil is displaced. This causes fairly high pressures to develop in the ground, with the result that the ground surface heaves in order to accommodate the displaced volume of soil. This heaving can cause damage to adjacent structures on the surface and to buried structures such as foundations, pipelines, etc. Using apparatus embodiments of the type shown in FIG. 4, in which the soil plug is removed from the ground, the volume of soil displaced outside the hole by the downward penetration of the mandrel is much less, for a given hole diameter. Hence, there is less trouble associated with heave of the ground surface and pressures within the ground on buried structures.

In the embodiments of FIGS. 1 through 4 the liquid flowing down from the surface reservoir has traveled wholly outside the exterior surface of the mandrel stem. In most practical applications of the present invention the liquid flows downward as shown in FIGS. 1 through 4 under the action of gravity in the space between the exterior of the mandrel and the soil walls of the hole. In some apparatus embodiments, however, other fluid channels are provided in addition.

One embodiment of this type is shown in FIG. 5 in which the mandrel 38d is a steel pipe with a series of holes 70 cut in the wall. At its lower end the mandrel is provided with a stiffener ring 64d and fits within the recess of an enlarged drive foot 42d which may be made of precast concrete as in the apparatus of FIG. 2. In this embodiment, as the mandrel penetrates downward, the liquid from the surface reservoir 50 not only flows down the annular space 46 but also enters the hollow interior through the holes 70 and flows down inside the mandrel. Hence, the liquid pressure inside the mandrel is essentially the same as the pressure outside of the same level, the only difference being the small head loss necessary to cause the liquid to flow through the holes 70 in the pipe walls. The holes in the walls of the pipe mandrel are made large enough so that the liquid can enter the interior of the mandrel easily and the head loss is small. A variation of this latter apparatus embodiment is shown in FIG. 6 in which a mandrel 38c consists of two concentric, spaced apart steel pipes 72 and 74. As seen in this figure the interior steel pipe 72 has no holes in it, so that the interior can be kept empty as the mandrel is being driven. The larger diameter exterior pipe 74 is rigidly and permanently attached to the interior pipe with steel webs 76 (FIG. 6b) and has holes 78 spaced apart along its walls. Hence, in this embodiment the liquid from the surface reservoir 50 travels downwardly as the mandrel is being driven in the exterior annular space 46 and also in the inner annular space 80 between the two concentric pipes 72 and 74. Again, as in the case of the hollow mandrel of FIG. the pressure in the liquid in the inner annular space is essentially the same as in the outer space, differing only by the head loss needed to cause the liquid to flow through the holes in the outer pipe 74.

The embodiment of FIG. 5 is particularly useful where the mandrel is pulled to leave behind a liquid filled hole, and when time on the job is a critical factor. The main advantage in this respect is that the interior of the pipe mandrel is filled completely by the time the mandrel has penetrated to the depth desired. Hence, the separate step of removing the pile driver from the upper end of the mandrel and filling the interior with liquid is eliminated. The method also eliminates the necessity for lifting the liquid into the air for the purpose of pouring it into the upper end of the pipe mandrel, which is generally protruding out of the ground a certain distance- Also, because the volume of the steel pipe itself is relatively small compared to the volume of the hole, the mandrel can be pulled rapidly, without the necessity of pouring an appreciable quantity of additional liquid to replace the volume of the mandrel as it is withdrawn, as required in the embodiment of FIG. lb.

A second advantage of the embodiments of FIGS. 5 and 6 is that a protected vertical channel is provided for downward flow of the liquid which will remain open, without any doubt, even though the soil might close in around the mandrel at some level. For example, in the circumstance where the man- 7 drel is being driven to a depth of 50 feet and where at a depth of 25 feet there is a layer of soil which has a strong tendency to close in around the mandrel, the use of apparatus embodiments as shown in FIG. 5 and 6 allows the liquid to flow downward into the ground and continue to fill the space as it is created by the downward penetrating drive foot 42, in spite of the fact that the soil at depth 25 feet may close off the outer annular space.

In the drawings showing embodiments of my invention discussed thus far I have shown generally how my method may be applied to make elongated structures in the ground in which a mandrel is used to form a hole and is then removed except for a detachable end member or drive foot that remains in the hole, after which the hole is filled with a liquid, such as concrete. The principles of my invention may also be applied in methods in which the drive foot is rigidly fixed to the mandrel and both are left in the ground to form part of the body of the structure. For example, in FIG. 7 a foundation piling 82 is shown, comprised of a steel beam stem 84, suchas an I-l-beam connected to a drive foot 42 consisting of a short length of heavy walled steel pipe 85 having a heavy steel plate 86 rigidly attached to its lower end, as by welding. This piling is driven in the same manner as shown in FIG. 1, a liquid 48 (concrete) being supplied at the ground level around the piling as it is driven and flowing downwardly by gravity to fill the space formed behind the drive foot.

FUNCTION AND QUALITY OF LIQUID USED OUTSIDE MANDREL prevents ground water from entering the hole. Second, the j liquid surrounds the mandrel stern andseparates it from the walls of the hole so that little or none of the energy of the pile driver is dissipated in overcoming friction between the mandrel stem and the soil. The liquid also serves other important functions in specific cases.

Depending primarily on the purpose for which the hole is being formed and the type of ground in which the hole is sunk; a number of different types of liquids are used. These are discussed hereinbelow when describing the special method steps used for the various applications. Except when used for the special purpose of chemical grouting as discussed later herein, it is a main general aspect of the present invention that once the liquid enters the ground it does not leave the hole in any significant quantity by seeping out into the soil surrounding the hole. Although in all soils the liquid may penetrate a short distance, and in some very coarse soils with large open pores, it may occasionally flow a considerable distance before being shut off, the properties of the liquid used are such that it essentially remains in the hole.

In general the liquid which enters the hole during the downward penetration of the mandrel must have two main properties. First, it must be sufficiently flowable so that it can flow down into the space at the same rate as the mandrel penetrates the ground, and the head loss in friction when flowing at this velocity must not be great; that is, it cannot have an excessively high viscosity and it cannot have appreciable internal friction. Second, it must have properties which will present large quantities of the liquid from flowing out into the surrounding ground. This latter property, of course, is dependent on the permeability of the ground. A thin liquid of low viscosity which might be unsatisfactory in one kind of ground because it flowed rapidly out into the pores of the soil may be perfectly satisfactory when used for construction in a more impervious type soil. In addition, the density of the liquid should be generally at least as heavy as water so that the pressure in the liquid column at any elevation will always be greater than the adjacent pressure in the ground water. This also depends somewhat on the situation. Since the pressure head in the liquid is always equalapproximately to the ground surface level and since the ground water table is generally considerably lower than this level, it is possible in some locations to use a liquid which has a density less than that of water and still maintain a pressure in the liquid-filled space greater than the ground water, especially if the ground water table is low.

In relatively impervious soils, such as homogeneous deposits of silts and clays, pure water can theoretically be used as the liquid and in a few practical applications water is quite satisfactory, as discussed later in this disclosure. Usually, however, other more suitable liquids are used to achieve special purposes.

In the general case the liquid must have one of several properties to prevent it from seeping easily out into the pores of the soil around the hole. Most satisfactory liquids for this purpose have one or more of the following properties: (1) thixotropy; (2) suspended clay or sand sized particles; (3) viscosity greater than water. The liquids used most commonly in practical applications of the principles of my invention have one or more of these properties. The most commonly used liquids are: colloidal mud consisting of a bentonitewater mixture of the kind normally used for a drilling fluid in a rotary drilling process; a self-disintegrating type of colloidal mud such as the product Revert manufactured by the Johnson Division of the Universal Oil Products Company, St. Paul, Minn.; and various cementitious grouts and fluid mortars, usually with a base of portland cement. In some applications the muds are weighted" with barite to increase the density and the liquid pressure in the hole. In other cases liquids consisting of a mixture of mud and silt or sand are used.

Liquids having the general aforesaid properties do not penetrate even very pervious soils very far and, hence, the liquid pressure acting in the space in the ground around the mandrel stem acts to support the soil walls of the hole as though there were an impervious skin on the surface. For example, it is well known that a colloidal mud such as a bentonite-water-slurry is thixotropic, and consequently it is very successful in supporting the walls of excavations in the ground below the water table. When such mud is first added to the hole there is a tendency for it to flow outwardly into the voids of the adjacent soil, since the fluid pressure in the mud is higher than the pressure in the ground water in the pores of the surrounding soil. As the mud penetrates a short distance into one of the small pores of the soil it gels because of the thixotropic action and does not penetrate further. Subsequently, driven by the difference in fluid pressure between the mud in the hole and the ground water, some of the water comprising the mud seeps into the adjacent ground leaving behind on the hole walls particles of pure bentonite. This action continues until a thin skin or cake" of bentonite lines the walls, which skin is almost completely impervious and acts as a lining against which the liquid pressure can be exerted to support and stabilize the walls of the hole. Grout slurries of port- Iand cement and water and fluid concretes act in much the same way; that is, the higher pressure in the fluid concrete placed into the hole tends to cause the water in the concrete to flow into the adjacent soil and to carry the particles of the cement and fine sand with it, which particles become wedged in the pores of the soil surrounding the hole creating a relatively impervious skin on the hole walls.

THE MANDREL AND I DRIVING HAMMER Many variations in the basic apparatus and methods can be used to make elongated structures in the ground according to the principles of the invention. For example, the invention does not depend on the mechanism by which the mandrel is caused to penetrate the ground. Any kind of a pile driving hammer, vibrating pile driver, sonic pile driver, or any other means which can push a mandrel into the ground can be used. In certain soft soils, the mandrel is caused to penetrate the ground simply under the action of a heavy static weight.

The mandrel can have an internal opening such as a pipe as shown in FIGS. 2, 3 and 4 or it can be solid as shown in FIG. 1, and it can have any convenient cross-sectional shape. The mandrel can be withdrawn from the hole or it can be left in place in the ground. The drive foot can be firmly fixed to the lower end of the mandrel or it can be detachably fixed during the driving process and left in place at the bottom of the hole when the mandrel is withdrawn. For many important applications the hole is formed by displacing the soil in the path of the downward penetrating mandrel outward into the ground directly surrounding the hole, as shown in FIGS. 1, 2 and 3. Alternatively, using a hollow pipe mandrel, some or all of the soil in the path of the downward penetrating mandrel is caused to move inwardly and to enter the interior of the hollow mandrel, as shown in FIG. 4. The soil which enters the interior of the mandrel can be left in place in the mandrel in the ground as a part of the structure so formed, or it can be removed from the ground from the interior of the mandrel using a number of means as described herein.

THE DRIVE FOOT ON THE MANDREL.

The drive foot on the lower end of the mandrel, which makes the actual hole in the ground in the procedures according to my invention, can be made of a variety of shapes and materials. Such drive members are also known in the art by a number of names such as drive shoe, boot, tip, drive point, etc. In this disclosure I will use the general descriptive term drive foot or enlarged drive foot. In the various embodiments of my invention discussed above, I have already shown enlarged drive foot members 42 consisting of a sleevelike shoe of cast steel in FIG. 1, the solid precast concrete drive foot 42a of FIG. 2, the heavy walled steel pipe with a heavy steel plate welded on its bottom, shown in FIG. 7, and the detachable steel annulus of FIG. 4.

In the embodiments of my apparatus in which the end of the mandrel is closed, the hole is formed in the ground by a process of pushing the soil in the path of the downward mandrel to the side. This is generally a process of overcoming the shearing resistance in the body of soil located in the path of the downward penetrating mandrel and in the zone immediately around the hole so formed. In many soil deposits, it is sufficiently accurate to describe this as an irreversible action in the sense that once the soil is sheared and pushed to the side there is no great tendency for it to be pushed back into its original position, and what little tendency it has to do so is easily resisted by the pressure of the liquid installed in the hole according to the principles ,of my invention. In fact, it is essentially valid to state that the present invention is based in large part on the discovery that in most soil deposits the hole formed by pushing the soil aside with a downward penetrating drive foot can be made to remain open if it is filled with liquid with a pressure equal to the approximate weight of a liquid column extending to the ground surface.

Another part of my invention was the discovery that the length of the enlarged drive foot did not need to be very great to prevent the hole from squeezing closed at a given level in the ground after the drive foot had penetrated downwardl In some soils, especially above the water table and in the upper 20 feet or less of depth, it is not imperative to use a liquid in the hole to prevent the walls from caving because the soil itself has sufficient cohesive strength to keep the hole open. In such circumstances, it is possible to drive a mandrel with an enlarged foot, such as shown in FIG. I, and form a hole in the ground which will stay open at least temporarily, even if no liquid is caused to fill the hole. Obviously, in soils of this type, and in similar soils that are not quite as stable, the length of the enlarged foot needs only to be a few inches to serve its purpose of pushing the soil out of the way to form the hole. For most practical applications, I use a minimum length for the enlarged drive foot in the range between 50 and percent of its outside diameter. I have found that this is satisfactory for most subsoil conditions, though in some very stable soils as discussed above, the drive foot may be a simple circular flat steel plate with a thickness of I inch or less.

In some soils, particularly below the water table, the act of forming the hole by pushing the soil to the side causes the development of fairly high pressures in the ground around the lower end of the mandrel. These pressures tend to squeeze in on the hole at any given level and reduce its diameter after the drive tip has penetrated beyond this level. In most cases these high pressures are the result of temporary pressures created in the water which fills the soil pores, commonly called pore water pressures. In the great majority of cases the soil and water pressure is only high for a short time and for a short I distance of the hole directly above the downward moving drive foot. I have found that a drive foot with a length equal to two to four times the diameter of the mandrel stem is adequate in the great majority of cases to prevent squeezing of the hole. In some circumstances, it is desirable to make the length of the enlarged drive foot longer, such as 7 to 10 times the diameter of the hole being formed.

The tendency for the hole to squeeze back and close is a function of the soil type, and particularly its permeability and water content, the diameter of the hole, the depth of the hole, and the number of other holes being put down in the immediately adjacent area. In extreme circumstances it is not practical to penetrate the ground below a certain depth using the embodiments in which the soil is pushed to the side without the hole closing in around the mandrel stem. In such a situation, if it is desirable to go to greater depths using the principles of the invention, a hollow cylindrical mandrel is used and the soil in the path of the downwardly penetrating drive tip is caused to enter the mandrel interior, as shown in FIG. 4. When using this apparatus embodiment, the enlarged drive foot need only have a length of a few inches, as shown in FIG. 4, even when penetrating soils of the type in which holes have the greatest tendency to squeeze.

It is seen in the above discussion of FIGS. 1 through 4 that in many practical applications of the present invention the mandrel stem consists of a heavy walled steel pipe or a circular 

1. A method of forming a sand drain in the ground comprising the steps: providing a mandrel having a straight stem and a detachable drive foot at or near its lower end, said drive foot having a cross-sectional area in the direction transverse to the mandrel axis which is larger than the transverse cross-sectional area of the solid portion of the mandrel stem; moving said mandrel stem downwardly to cause said drive foot to penetrate into the ground so that an elongated hole is formed, the area of which hole is larger than the cross-sectional body area of the mandrel, thus creating longitudinal space in the ground adjacent the mandrel stem behind said downward penetrating drive foot; causing a liquid to flow downwardly from the ground surface into said longitudinal space simultaneously with the downward mandrel penetration so that at least a portion of this space is immediately filled with liquid as soon as it is created, said liquid serving to prevent the soil or ground water from the walls of the hole from entering said space; withdrawing said mandrel from the ground while simultaneously causing an additional supply of liquid to flow into the hole in such a way that the volume of the mandrel being withdrawn is replaced with liquid, leaving the detachable drive foot fixed in the ground at the bottom of the liquid-filled hole; filling said liquid-filled hole with sand by pouring it in from the surface.
 2. A method of forming a sand drain in the ground comprising the steps: providing a mandrel having a straight stem with a hollow interior and a detachable drive foot at or near its lower end, said drive foot having a central opening and cross-sectional area in the direction transverse to the mandrel axis which is larger than the transverse cross-sectional area of the solid portion of the mandrel stem; moving said mandrel stem downwardly to cause said drive foot to penetrate into the ground so that an elongated hole is formed, having an area larger than the cross-sectional body area of the mandrel, thus creating longitudinal space in the ground adjacent the mandrel stem behind said downward penetrating drive foot, and so that some of the soil lying in the path of the downward penetrating mandrel enters the interior of said mandrel stem in the form of a soil plug, said soil plug inside said mandrel being carried out of the hole along with said mandrel stem; causing said longitudinal space to be filled with liquid simultaneously with the downward mandrel penetration so that at least a portion of this space is immediately filled with liquid as soon as it is created, said liquid serving to prevent the soil or ground water from the walls of the hole from entering said space; withdrawing said mandrel from the ground while simultaneously causing an additional supply of liquid to flow into the hole in such a way that the volume of the mandrel being withdrawn is replaced with liquid leaving the detachable drive foot fixed in the ground at the bottom of the liquid-filled hole; filling said liquid-filled hole with sand by pouring it in from the surface.
 3. The method as described in claim 2 including the further step of removing said soil which enters the hollow interior of said mandrel progressively as the mandrel enters the ground.
 4. The method as described in claim 3 in which said soil plug is removed from the interior of said mandrel by blowing it out with compressed air.
 5. The method as described in claim 2 wherein said mandrel stem is a hollow tubular member having holes spaced apart along its length and said drive foot is an annulus with a central opening, said soil plug having an outside diameter smaller than the inside diameter of the mandrel stem, said water flowing through the holes in the walls of said mandrel stem filling the annular space created between the soil plug and the interior of said mandrel stem during its downward travel.
 6. A method of forming a sand drain in the ground comprising the steps: providing a mandrel with a straight hollow tubular stem and a detachable drive foot at or near its lower end, the exterior dimensions of said drive foot in the direction transverse to the mandrel axis being larger than the exterior diameter of the mandrel stem, said detachable drive foot also having a central opening; moving said mandrel stem downwardly to cause said drive foot to penetrate into the ground so that an elongated hole is formed with a cross-sectional shape the same as the exterior shape of said drive foot and larger than said mandrel stem, thus creating longitudinal space in the ground adjacent the exterior surface of said mandrel stem behind said downward penetrating drive foot, some of the soil lying in the path of the downward penetrating mandrel entering the interior of the mandrel stem through said drive foot central opening in the form of a soil plug; causing said longitudinal space that is exterior of said mandrel stem to be filled with liquid simultaneously with downward mandrel penetration, said liquid serving to prevent soil or ground water from the walls of the hole from entering said space, said liquid being a flowable mixture of sand and self-disintegrating mud; withdrawing said mandrel stem from the ground, said soil plug inside the mandrel being carried out of the ground with the mandrel stem, while simultaneously causing an additional supply of the same liquid to flow into the hole in such a way that the voLume of the mandrel and soil plug being withdrawn is replaced with the liquid, leaving the detachable drive foot fixed in the ground at the bottom of the liquid-filled hole.
 7. The method of claim 6 including the further step of moving said soil which enters the hollow interior of said mandrel stem progressively as the mandrel penetrates the ground.
 8. The method as described in claim 7 in which said soil is removed from said mandrel interior by blowing it out with compressed air.
 9. The method as described in claim 6 wherein said mandrel stem has holes spaced apart along its length and said soil plug has a diameter smaller than the inside diameter of the mandrel stem, said liquid flowing through said holes in the walls of the mandrel stem filling the annular space created between the soil plug and the interior of the mandrel stem during the downward penetration of the mandrel into the ground.
 10. The method as described in claim 6 in which said soil plug is left behind in the ground when the mandrel is withdrawn, said sand drain being formed with a tubular shape.
 11. A method of forming a sand drain in the ground comprising the steps: providing a mandrel having a straight stem and a detachable drive foot at or near its lower end, said drive foot having a cross-sectional area in the direction transverse to the mandrel axis which is larger than the transverse cross-sectional area of the solid portion of the mandrel stem; attaching one end of a porous conduit to said drive foot, said porous conduit having a length approximately equal to that of the sand drain being formed; moving said mandrel stem downwardly to cause said drive foot to penetrate into the ground so that an elongated hole is formed, the area of which hole is larger than the cross-sectional body area of the mandrel, thus creating longitudinal space in the ground adjacent the mandrel stem behind said downward penetrating drive foot and carrying said porous conduit into the ground inside said elongated hole; causing liquid to flow into said space simultaneously with downward mandrel penetration so that at least a portion of the space is immediately filled with liquid as soon as it is created, said liquid serving to prevent soil or ground water from the walls of the hole from entering said space, said liquid being a flowable mixture of sand and self-disintegrating mud; withdrawing said mandrel stem from the ground while simultaneously causing an additional supply of the same liquid to flow into the hole in such a way that the volume of the mandrel being withdrawn is replaced with the liquid, leaving the detachable drive foot fixed in the ground at the bottom of the liquid-filled hole and leaving said porous conduit centrally located in the liquid-filled hole extending at least to the ground surface.
 12. A method of creating a sand-filled cavity below ground comprising the steps: providing a mandrel having a straight stem and a detachable drive foot at or near its lower end, said drive foot having a cross-sectional area in the direction transverse to the mandrel axis which is larger than the transverse cross-sectional area of the solid portion of the mandrel stem; moving said mandrel stem downwardly to cause said drive foot to penetrate into the ground so that an elongated cavity is formed, the area of which is larger than the cross-sectional body area of the mandrel, thus creating longitudinal space in the ground adjacent the mandrel stem behind said downward penetrating drive foot; simultaneously filling said cavity with a fluid mixture of sand a viscous liquid, which fluid mixture has sufficient pressure to prevent collapse of the cavity, said viscous liquid having the characteristic that its viscosity decreases with time and gradually approaches the viscosity of water, said mixture within said cavity being left in place while the viscosity of said liquid decreases, thereby eventually leaving the cavity filled only with sand and a liquid having a viscosiTy essentially that of water.
 13. The method of claim 12 in which said viscous liquid is a self-disintegrating mud comprising: a mixture of water and an organic substance with some form of bacteria or enzymes which cause the organic substance to self-destruct within a few days.
 14. The method as described in claim 13 including the extra step of placing a porous tubing having a smaller diameter than the diameter of said cavity and positioning it centrally inside said cavity. 